Large tractors or trucks (e.g., semi-tractors) are commonly used to transport cargo within a trailer or container. Existing tractors in a tractor-trailer combination typically include a sleeper cabin for the occupant (e.g., driver or passenger) to rest during a journey. Auxiliary power units (APUs) are used with semi-tractors to provide power to the sleeper cabin when the primary power source (e.g., tractor engine, high voltage battery source, etc.) is turned off (i.e., deactivated). This can reduce fuel consumption, maintenance costs, emissions, and noise generated by not requiring the tractor main power source to operate (e.g., idle when the main power source is a tractor engine) during occupant rest periods or other periods of vehicle non-movement.